Leadframes used in semiconductor packages as chip carriers are patterned metal sheets including a plurality of metal leads, which have the advantages of lower packaging costs where chips are attached on leadframes and then are encapsulated by encapsulants. The semiconductor packages are mounted to external printed circuit boards through the external portions of the leads of leadframes. In order to form encapsulants by molding, the leads of leadframe are extended outside the molding area to be clamped by top and bottom mold tools. Moreover, leadframes are normally made by either etching or punching a metal sheet to form a plurality of leads.
Since the leads are formed from the same layer of a leadframe, the sequence of the leads is fixed and can not be changed for different pin assignments. Therefore, various methods have been disclosed to enable electrical paths from bonding pads of a chip to leads of leadframes to reroute pin assignments without being constrained by the sequent nature of the leads such as combining two leadframes, attaching a thin-film circuit on the active surface of a chip, or disposing electrically redistributing components, such as conductive bumps, redistributed traces, or comb-like conductive leads, on die-attaching tapes. However, there are extra costs to deposit a second leadframe or internal redistributing components on specific locations so that the packaging processes become more complicated with higher risks of exposing bonding wires from the encapsulant where package thickness is also increased. Moreover, the non-chip bonding ends of bonding wires will cause wire bonding height differences and displacement leading to constant adjusting of wire bonding parameters.